Japanese Unexamined Utility Model Publication No. 7-4248 discloses a lightweight type of baby carriage in which a seat hammock is mounted on a body frame. The baby carriage disclosed in the above document is folded so as to shrink in the width direction. A backrest sheet part of the hammock is supported by a belt member from behind and a reclined angle of the backrest sheet part can be varied by adjusting a length of the belt. According to this kind of baby carriage, a reclining structure of the backrest part is very simple and its weight can be reduced.
In general, the seat hammock has a core in each of a seating surface sheet part and the backrest sheet part. In the conventional lightweight type of baby carriage folded so as to shrink in the width direction, a seating surface core and a back surface core are separated so as not to hinder a folding operation. In addition, width dimensions of the seating surface core and the back surface core are considerably reduced so that the body frame can easily shrink in the width direction. In another case, the respective seating surface core and back surface core are constituted so as to be bent in the shape of wedge in the width direction so that the seating surface core and the back surface core can reduce their width dimensions together with the body frame.
When a child is seated in the seat of the baby carriage, a waist part of the child is held by a crotch belt and a waist belt provided in the baby carriage. Therefore, a movement of the seating surface sheet part supporting buttocks of the child from beneath can be restrained. Meanwhile, the backrest sheet part is connected to the seating surface sheet part by a cloth of the hammock only. Besides, since the width dimension of the back surface core is smaller than the width dimension of the backrest sheet part in general, the backrest sheet part is swayed from side to side by oscillations generated in accordance with movements of the baby carriage. Because of such lateral sway of the backrest sheet part, the child feels uncomfortable and a parent feels uneasy.